Transfer line

ABSTRACT

A transfer line between the outlet of a steam cracker and the inlet for the quench system has metallic or ceramic inserts having a pore size from about 0.001 to about 0.5 microns inside the line forming a gas tight barrier with the inner surface of the line and having a vent for the resulting gas tight pocket are used to separate H2, CH4, CO and CO2 from cracked gases reducing the load on the down-stream separation train of the steam cracker.

The present disclosure relates to cracking paraffins, for example C₂₋₄paraffins to olefins, including use of transfer line(s) between theoutlet of a cracking furnace and the inlet for the quench system whichis adapted to separate one or more of H₂, CH₄, CO, and CO₂ attemperatures from at least about 450° C., for example, from at leastabout 500° C., in some instances from about 700° C. to about 900° C.from the cracked gases.

In the back end of an ethylene steam cracker, a significant amount ofcapital equipment and energy is used to separate the components of acracked gas to obtain relatively pure ethylene, from methane and othercomponents including H₂, CO, and CO₂. If some or all of the H₂, CH₄, CO,and CO₂ could be separated from the cracked gases prior to entering theseparation train, it would reduce the load on the separation train.

U.S. Pat. No. 4,078,292 issued Mar. 14, 1978 to Porter, assigned toAllied Chemical Corporation, teaches a method of repairing a crackedtransfer line. The method involves cutting out the cracked portion ofthe transfer line and placing ceramics over the outside of the transferline and then sealing the repaired transfer line in a metal sheath. Thepatent does not disclose that one or more of H₂, CH₄, CO, and CO₂ couldbe separated from the cracked gas via the ceramic.

The transfer line disclosed in the 292 patent is conical and this isgenerally the shape of transfer lines used today. However, publishedU.S. Patent Application Publication No. 2014/0178610 in the name ofClavelle et al., assigned to NOVA Chemicals (International) S.A, thetext of which is herein incorporated by reference, teaches a transferline (transfer line exchanger) with a non-uniform passage in which notless than 5% of the flow passage from the furnace outlet to the inlet tothe quench system has an ARQ from 1.02 to 1.15. Rather than beingconical, the transfer line looks like a thicker oval line which ends ina non-symmetrical bell shape. In some embodiments, the systems andmethods disclosed herein would also be useful in such shaped transferlines.

There are a series of patents in the name of Ma et al., assigned to theWorcester Polytechnic Institute, illustrated by U.S. Pat. No. 7,727,596issued Jun. 1, 2010, that teach separating hydrogen from a gaseousmixture at temperatures up to about 500° C. The gas mixture appears tobe predominantly H₂ and helium. There is no discussion of separatinghydrogen from a gaseous mixture of hydrogen, CH₄, CO, CO₂ and olefins(ethylene). Interestingly, the patent discloses high temperature alloyshaving a pore size form 0.1 microns to 15 microns in some instances from0.1 to 0.5 microns, which may be used as substrates for the separationmembrane (Col. 7, lines 16-60).

U.S. Patent Application Publication No. 2015/0044130 published Feb. 12,2015 in the name of Tang et al., assigned to Bettergy teaches dopingzeolites with palladium to prepare a semi-permeable membrane useful attemperatures up to about 450° C. (see the tables in the examples). Thetables in the examples show a high selectivity for hydrogen overmolecules such as CO₂, and CH₄ at temperatures up to about 450° C. Thespecification does not teach or suggest the membranes would be useful attemperatures above 450° C.

U.S. Pat. No. 8,791,037 issued Jul. 29, 2014 to Berchtold et al.,assigned to the U.S. Department of Energy, discloses a non oxide(Si/C/N) ceramic membrane stable at temperatures up to about 1000° C.The specification teaches the pore size may be controlled by monomercomposition, comonomer functionality, photopolymerization conditions andpyrolysis conditions (Col. 6, lines 40-50). However, no details of theconditions are disclosed in the patent.

In some embodiments, the present disclosure seeks to provide a method toseparate one or more of H₂, CH₄, CO, and CO₂ from a stream of crackedgases leaving a steam cracker prior to entering the quench system.

In one embodiment provided herein, is a transfer line between the outletof a steam cracker and the inlet to a quench exchanger comprising:

-   -   i) a continuous passageway of a metal having a melting        temperature greater than 1000° C. having a flange at one end of        the passageway adapted to cooperate with the outlet from a steam        cracking furnace and a flange at the opposite end of the        passageway adapted to cooperate with the inlet to a quench        exchanger; one or more inserts in said passageway permitting the        flow of gases through said passageway, said inserts being        permeable to at least one of H₂, CH₄, CO, and CO₂ at        temperatures from 500° C. to 900° C. and spaced from the        interior wall of the passageway and sealed to the interior wall        of said passageway to provide one or more gas tight chambers;        and one or more ports through the metal to withdraw gases from        said one or more gas tight chambers;

-   said inserts being selected from:    -   a) ceramic inserts having a melting point greater than 900° C.        and a porosity from 5 to 75% of pores having a size from 0.001        microns to about 5 microns, for example from 0.01 to 0.5 microns        and fitting within the metal casting and    -   b) metal inserts having a porosity from 5 to 75% of pores having        a size from 0.001 microns to about 5 microns for example from        0.01 to 0.5 microns;    -   c) or both; and optionally    -   ii) a membrane permeable to at least one of H₂, CH₄, CO, and CO₂        at temperatures from 500° C. to 900° C. on elements a), b) or        both to permit the passage of at least one of H₂, CH₄, CO, and        CO₂ there through into the gas tight chamber.

In a further embodiment, the insert is a porous ceramic formed fromoxides, dioxides, nitrides, carbides and phosphates selected from poroussilicon dioxide, fused silicon dioxide, porous aluminum oxide, titaniumdioxide, zirconium dioxide, thorium dioxide, lanthanum oxide, magnesiumoxide, calcium oxide, barium oxide, tin oxide, cerium dioxide, zincoxide, boron oxide, boron nitride, boron carbide, boron phosphate,zirconium phosphate, yttrium oxide, aluminum silicate, silicon nitride,silicon carbide and mixtures thereof.

In a further embodiment, the ceramic insert is resistant to coking.

In a further embodiment, the ceramic insert is in the shape of a cone oran island.

In a further embodiment, the insert is a metal alloy comprising one ormore of iron, nickel, titanium, chromium, aluminum, and molybdenum.

In a further embodiment, the metal insert is resistant to coking.

In a further embodiment, the metal insert is in the shape of a cone oran island. In a further embodiment, the membrane is present and has athickness from 0.1 to 10 microns.

In a further embodiment, the membrane comprises one or more metalsselected from Pd, Ta, V, Pt, Nb, and Zr.

In a further embodiment, the membrane further comprises one or moremetal oxide ceramic selected from Al₂O₃, BaTiO₃, SrTiO₃ and ZrO₂.

In a further embodiment, the membrane is a dense metal oxide membrane.

In a further embodiment, in the membrane the metal comprises Pd.

In a further embodiment, the metal oxide comprises yttria stabilizedZrO₂

In a further embodiment, the metal oxide comprises calcia stabilizedZrO₂

In a further embodiment, the membrane is not less than about 95% oftheoretical density.

In a further embodiment, the membrane is coated on component a).

In a further embodiment, a) comprises an alumina ceramic.

In a further embodiment, the membrane is coated on component b).

In a further embodiment, intermediate the ceramic oxide and component b)is a ceramic comprising one or more particles selected from tungsten,alumina oxide, zirconia, titania, silicon carbide, chromium oxide,yttrium oxide, having a particles size from 0.01 to 5 microns.

In a further embodiment, the membrane is Si/C/N ceramic formed by:combining a monomeric and/or oligomeric silazane ceramic precursor witha comonomer comprising one or more of the group consisting of ene(vinyl) functionalized, oligomeric, inorganic or organic silazanes,difunctional thiols, and tetrafunctional thiols;

-   forming the combination as a thin film on a substrate;    photopolymerizing the thin film; and-   pyrolyzing the photopolymerized thin film so as to result in a    ceramic membrane that contains substantially no oxide.

In a further embodiment, said monomeric and/or oligomeric silazanescontain heteroatoms selected from boron, titanium, aluminum, phosphorus,and combinations thereof.

In a further embodiment, provided herein is a method to remove one ormore of H₂, CH₄, CO, and CO₂ from cracked gases leaving a crackingfurnace by passing the gases through a transfer line as above attemperatures from 500° C. to 900° C.

In a further embodiment, provided here in is a cracking furnace andquench system for cracked gases comprising intermediate the exit of thecracking furnace and the quench system a transfer line as above.

Numbers Ranges:

Other than in the operating examples or where otherwise indicated, allnumbers or expressions referring to quantities of ingredients, reactionconditions, etc. used in the specification and claims are to beunderstood as modified in all instances by the term “about.”Accordingly, unless indicated to the contrary, the numerical parametersset forth in the following specification and attached claims areapproximations that can vary depending upon the properties that thepresent disclosure desires to obtain. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical values, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between andincluding the recited minimum value of 1 and the recited maximum valueof 10; that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10. Because the disclosednumerical ranges are continuous, they include every value between theminimum and maximum values. Unless expressly indicated otherwise, thevarious numerical ranges specified in this application areapproximations.

All compositional ranges expressed herein are limited in total to and donot exceed 100 percent (volume percent or weight percent) in practice.Where multiple components can be present in a composition, the sum ofthe maximum amounts of each component can exceed 100 percent, with theunderstanding that, and as those skilled in the art readily understand,that the amounts of the components actually used will conform to themaximum of 100 percent.

In steam cracking of paraffins such as naphtha and lower alkanes such asC₂₋₄ paraffins, the feed together with steam is fed into tubes or coilspassing through a convection section of the cracker where the feed isheated to close to cracking temperatures (about 750° C.). The feed thenpasses through coils in the radiant section of the furnace in a timefrom about 0.001 to 2.0 seconds, in some embodiments, from 0.001 to 1second. In the radiant section of the furnace, wall mounted burners andor floor mounted burners heat the walls to a temperature where theyradiate heat onto the coil surfaces. The temperature of the coil is inthe range from about 800° C. to about 975° C. At these temperatures, themolecules are cracked, for example ethane is converted into ethylene.The composition of the gases leaving the furnace contain many speciesincluding free radicals and need to be quenched quickly to preventfurther rearrangement of the molecules in the stream. The cracked gasstream passes through a transfer line to a heat exchanger where the gasis quickly quenched to a temperature to prevent any significantrearrangement of the molecules in the gas. The quenched gas then entersa separation train. In the separation train, the gas is sequentiallycooled to low temperatures to condense methane, ethane and propane, andraffinates and other co-products. The co-products may include acetyleneand other heavier products such as benzene, toluene and xylene (BTX).The product stream from the cracker also contains hydrogen, methane,carbon monoxide and carbon dioxide. These components also are cooled andpassed through parts of the separation train. This puts an extra load onthe separation train. In some embodiments, it is desirable to reduce theamount of H₂, CH₄, CO and CO₂ in the cracked gases prior to entering theseparation train.

In accordance with the present disclosure, there is provided a transferline between the outlet of a steam cracker and the inlet to a heatexchanger (quench system) comprising a continuous passageway of a metalhaving a melting temperature greater than 1000° C. having a flange atone end of the passageway adapted to cooperate with the outlet from asteam cracking furnace and a flange at the opposite end of thepassageway adapted to cooperate with the inlet of a tube and shell heatexchanger or a quench system; one or more inserts in said passagewaypermitting the flow of gases through said passageway said inserts beingpermeable to at least one of H₂, CH₄, CO, and CO₂ at temperatures from500° C., for example, from 550° C. to 900° C. being spaced from theinterior wall of the passageway and sealed to the interior wall of saidpassageway to provide one or more gas tight chambers; and one or moreports through the metal to withdraw gases from said one or more gastight chambers. In some embodiments it is desirable to minimize thediffusion of ethane and ethylene through the membranes to as low aspossible. In some instances, the concentration of ethane and ethylene inthe permeate stream should be less than 10 wt %, for example less than 5wt. %, or for example less than 2 wt %, or for example less than 1 wt %,or in another example less than 0.5 wt. %.

The transfer line is typically cast from a metal having a melting pointgreater than 1000° C., for example greater than 1100° C. The transferline may be made of any high temperature steel. In some embodiments, thetransfer line is a stainless steel which may be selected from wroughtstainless, austentic stainless steel and HP, HT, HU, HW and HX stainlesssteel, heat resistant steel, and nickel based alloys. The transfer linemay be a high strength low alloy steel (HSLA); high strength structuralsteel or ultra-high strength steel. The classification and compositionof such steels are known to those skilled in the art.

Further examples of suitable metal components include, but are notlimited to, iron, nickel, titanium, chromium, aluminum, and alloysthereof, e.g., steel, stainless steel, HASTELLOY® alloys (e.g.,HASTELLOY® C-22®) (trademarks of Haynes International, Inc., Kokomo,Ind.) and INCONEL® alloys (e.g., INCONEL® alloy 625) (INCONEL is atrademark of Huntington Alloys Corp., Huntington W. Va.). In oneembodiment, the transfer line includes an alloy containing chromium andnickel (e.g., INCONEL® alloy 625). In an additional embodiment, thealloy contains chromium, nickel and molybdenum such as, for example,HASTELLOY® C-22® or INCONEL® alloy 625.

In one embodiment, the stainless steel, for example heat resistantstainless steel, comprises, for example, from 13 to 50, or for example,20 to 50, or for example, from 20 to 38 weight % of chromium. Thestainless steel may further comprise from 20 to 50, for example from 25to 50, or for example, from 25 to 48, for example from about 30 to 45weight % of Ni. The balance of the stainless steel may be substantiallyiron.

In some embodiments, the steel may further comprise a number of traceelements including at least 0.2 weight %, up to 3 weight %, for example,1.0 weight %, up to 2.5 weight % or for example not more than 2 weight %of manganese; from 0.3 to 2, or, for example, 0.8 to 1.6, or less than1.9 weight % of Si; less than 3, or less than 2 weight % of titanium,niobium (for example less than 2.0, or for example less than 1.5 weight% of niobium) and all other trace metals; and carbon in an amount ofless than 2.0 weight %. The trace elements are present in amounts sothat the composition of the steel totals 100 weight %.

In one embodiment, the stainless steel, for example heat resistantstainless steel comprises from 13 to 50, or for example 20 to 50, or forexample from 20 to 38 weight % of chromium. The stainless steel mayfurther comprise from 20 to 50, or for example from 25 to 50 or forexample from 25 to 48, or for example from about 30 to 45 weight % ofNi. The balance of the stainless steel may be substantially iron.

Some embodiments of the disclosure may also be used with nickel and/orcobalt based extreme austentic high temperature alloys (HTAs). In someembodiments, the alloys comprise a major amount of nickel or cobalt. Insome embodiments, the high temperature nickel based alloys comprise fromabout 50 to 70, or for example from about 55 to 65 weight % of Ni; fromabout 20 to 10 weight % of Cr; from about 20 to 10 weight % of Co; andfrom about 5 to 9 weight % of Fe and the balance one or more of thetrace elements noted below to bring the composition up to 100 weight %.In some embodiments, the high temperature cobalt based alloys comprisefrom 40 to 65 weight % of Co; from 15 to 20 weight % of Cr; from 20 to13 weight % of Ni; less than 4 weight % of Fe and the balance one ormore trace elements as set out below and up to 20 weight % of W. The sumof the components adding up to 100 weight %.

In some embodiments, the steel may further comprise a number of traceelements including at least 0.2 weight %, up to 3 weight % or forexample 1.0 weight %, up to 2.5 weight % or in another example not morethan 2 weight % of manganese; from 0.3 to 2, or for example 0.8 to 1.6or in another example less than 1.9 weight % of Si; less than 3, or lessthan 2 weight % of titanium, niobium (for example less than 2.0, or lessthan 1.5 weight % of niobium) and all other trace metals; and carbon inan amount of less than 2.0 weight %. The trace elements are present inamounts so that the composition of the steel totals 100 weight %.

Some embodiments of the disclosure are used with a transfer line havinga good resistance to coke make, for example such as those disclosed inU.S. Pat. No. 6,436,202 issued Aug. 20, 2002 to Benum et al., assignedto NOVA Chemicals (International) S.A. In some embodiments, the run timebetween decoking the transfer line should be greater than 90 days, forexample greater than 180 days or for example greater than 200 days.

The transfer line is, in some embodiments, cast as a single piece havinga continuous impermeable wall to the gases separated from the crackedgas stream. In some instances, the transfer line could be cast as partsor portions of the line particularly where the line is as disclosed inU.S. Pat. No. 9,273,805 issued Jun. 26, 2014 to Clavelle et al.,assigned to NOVA Chemicals (International) S.A.

In some embodiments, the transfer line could be conical, cast in twolongitudinal half sections to be joined together. The joint needs to begas tight.

Inside at least a portion of the transfer line are one or more insertspermeable to the passage of at least one of H₂, CH₄, CO, and CO₂ therethrough at temperatures from 500° C., for example from 550° C. to 900°C. in the passageway, not substantially blocking or obstructing thepassage way, permitting the flow of gases through the passageway theinserts being spaced from the interior wall of the passageway and sealedto the interior wall of said passageway to provide one or more gas tightchambers. Not substantially blocking or obstructing the passage waymeans not blocking the passageway by more than 15%, in some embodimentsless than 10%, in further embodiments less than 5% (e.g., by crosssection of the passage). The insert could be a cast conical inserthaving a central passage way there through. In which case, the entireconical insert would be permeable to one or more of H₂, CH₄, CO, andCO₂. The insert could be a deformed cone as in the outlet of thetransfer line disclosed in U.S. Pat. No. 9,273,805 having a centralpassage way there through. In some embodiments, the insert need not becone shaped but would provide a round or elliptical “island” on the sideof the interior wall of the transfer line. In some embodiments, whensuch “islands” are used, they are spaced so that there is still an openflow passage through the transfer line. The inserts are joined to theinterior wall of the transfer line to provide a gas tight seal.

In some embodiments, the inserts may be ceramic. In some embodiments,the ceramic is stable at temperatures not less than 450° C. or forexample not less than 500° C., or in some embodiments not less than 550°C., or in another example from 850° C. to 900° C. or in yet anotherexample up to 1000° C. The ceramic should be porous ceramic formed fromoxides, dioxides, nitrides, carbides and phosphates selected from poroussilicon dioxide, fused silicon dioxide, porous aluminum oxide, titaniumdioxide, zirconium dioxide, thorium dioxide, lanthanum oxide, magnesiumoxide, calcium oxide, barium oxide, tin oxide, cerium dioxide, zincoxide, boron oxide, boron nitride, boron carbide, boron phosphate,zirconium phosphate, yttrium oxide, aluminum silicate, silicon nitride,silicon carbide and mixtures thereof. In some embodiments, the ceramicmembrane may be a dense gas-selective membrane as described below.

Exemplary components for forming ceramic membranes include oxides oftitanium, zirconium, aluminum (e.g., alpha alumina and gamma alumina),magnesium, silicon and mixtures thereof. Ceramics of mixed alumina andsilicon oxide are zeolites and the titanium equivalents are ETS typeceramics. The pore size in the structure of the ceramic material may befrom 0.001 to 1 micron in some embodiments from 0.01 to 0.5 microns.This pore size is sufficient to permit one or more of H₂, CH₄, CO andCO₂ to diffuse or permeate through the ceramic. However, it should benoted the ceramic need not necessarily be compacted to excludeinterstitial spaces, so that the gases extracted from the cracked gasstream could also pass through the interstitial spaces in the castceramic.

In some embodiments, the ceramic may be doped with or contain,particles, fibers or whisker of a metal that helps transport one or moreof hydrogen, methane, carbon monoxide and carbon dioxide. Palladium,niobium, tantalum, zirconium, vanadium and alloys thereof may be usedfor these purposes.

The pore size of the ceramic must be large enough to permit a moleculeselected from hydrogen, methane, carbon monoxide and carbon dioxide topass through the ceramic particles. The internal pore sized of theceramic particles may range from 0.0003 to 1.0 microns or larger.

In some embodiments, the ceramic inserts may have a non-coking or lowcoking surface such as a sodium aluminum complex.

The inserts may also be a metal or alloy having a melting point above450° C., or for example above 500° C. or for example above 900° C., orfor example above 1000° C., or in another example above 1050° C. Theporous metal can be formed from any of a variety of components known tothose of ordinary skill in the art. Examples of suitable metal or alloycomponents include, but are not limited to, iron, nickel, titanium,chromium, aluminum, and alloys thereof, e.g., steel, stainless steel,HASTELLOY® alloys (e.g., HASTELLOY® C-22®) (trademarks of HaynesInternational, Inc., Kokomo, Ind.) and INCONEL® alloys (e.g., INCONEL®alloy 625) (INCONEL is a trademark of Huntington Alloys Corp.,Huntington W. Va.). In one embodiment, the porous substrate includes analloy containing chromium and nickel (e.g., INCONEL® alloy 625). In anadditional embodiment, the alloy contains chromium, nickel andmolybdenum such as, for example, HASTELLOY® C-22® or INCONEL® alloy 625.The porous metal can be porous stainless steel. Porous stainless steelthat is suitable for use as substrates are available from MottMetallurgical Corporation (Farmington, Conn.) and from Pall Corporation(East Hills, N.Y.), for example.

One of ordinary skill in the art can select substrate thickness,porosity, and pore size distribution using techniques known in the art.Desired substrate thickness, porosity and pore size distribution can beselected based on, among other factors, the operating conditions of thefinal composite gas separation module such as operating pressure.Substrates having generally higher porosities and generally smaller poresizes are particularly suited for producing composite gas separationmodules. In some embodiments, the substrate can have a porosity in arange of about 5 to about 75% or about 15 to about 50%. While the poresize distribution of a substrate can vary, the substrate can have porediameters that range from about 0.001 microns or less to about 15microns or for example from 0.01 to 5 microns, or in another examplefrom 0.1 to 0.5 microns.

In some embodiments, smaller pore sizes are preferred. However, in someembodiments, a substrate having larger pores is used and an intermediatelayer having generally smaller pore sizes is formed on the poroussubstrate (e.g., a graded support is formed).

In some embodiments, the mean or median pore size of the substrate canrange from about 0.001 to about 15 microns, e.g., from about 0.01 micronto about 1, 3, 5, 7 or about 10 microns. For example, the substrate canbe an about 0.1 micron grade substrate to an about 0.5 micron gradesubstrate, e.g., 0.01 micron, 0.2 micron, and 0.5 micron grades ofstainless steel substrates can be used.

Both the ceramic and metallic inserts may optionally be coated with agas-selective membrane.

In one embodiment, the gas selective membrane is a dense gas-selectivemembrane selectively permeable to hydrogen, and can include one or morehydrogen-selective metals or alloys thereof. Hydrogen-selective metalsinclude, but are not limited to, niobium (Nb), tantalum (Ta), vanadium(V), palladium (Pd), platinum (Pt), zirconium (Zr) andhydrogen-selective alloys thereof. In some embodiments, palladium andalloys of palladium are preferred. For example, palladium can be alloyedwith at least one of the metals selected from gold, platinum, ruthenium,rhodium, yttrium, cerium and indium. Some care needs to be exercised inselecting components to use in the alloys. Copper and silver have beensuggested as alloy components. However, as cracked gas may containacetylene and steam one would avoid silver and copper as alloycomponents as there may be a tendency to form silver of copper acetylidewhich present an explosive hazard. The metallic component may have aparticle size from about 0.3 to about 3 microns.

The dense gas-separation membrane can include one or more componentsthat are not gas-selective materials, e.g., components that are nothydrogen-selective materials such as metal oxide ceramics. Examples ofsome useful metal oxide ceramics are alumina (Al₂O₃), barium titanate(BaTiO₃), strontium titanate (StTiO₃), zirconia ZrO₂) stabilized orpartially stabilized with yttria or calcia and various combinationsthereof. When used, the metal oxide ceramic may be present in an amountof from 10 to 90 wt. %, or from 30 to 70 wt. % or for example from 40wt. % to 60 wt. % of the blend of the metal and metal oxide ceramic.

The dense gas-selective membrane may have a thickness from about 0.1 to10 microns. For example, in one embodiment, the thickness of the densegas-selective membrane is less than about 10 microns such as about 3 to8 microns, in some embodiments less than 0.5 microns. In someembodiments the membrane is a uniform thickness which means thethickness across the membrane may vary by about +/−1 micron, or lessthan about +/−1 micron.

In some embodiments the metal components for the dense gas—selectivemembrane are activated by bringing them into contact with a solution ofSnCl₂ (e.g., 1 g/l pH approximately 2) then filtering the powder fromthe solution shortly after contact and washing it and optionally dryingit to obtain the activated metal (PdCl₂). The activated metal togetherwith the metal oxide ceramic, if present, may be used as a powder ordispersed (slurry) or re-dissolved in a suitable solvent or diluent(e.g., water).

A layer of particulate material to form the dense gas phase selectivemembrane is brought into contact with the upper or outer surface of theporous ceramic or metal inserts (relative to the flow path of thecracked gas) by any suitable method known to those skilled in the artfor applying a particulate material (e.g., powder) to a porous surface.For example, the particulate material may be applied to the surface ofthe porous insert by transport with a gas, or by application of a paste,a slurry or suspension of the particulate material, or by pressing orrubbing a powder of the particulate materials upon the surface of theporous insert.

In one embodiment, at least one of the contacting steps is conductedwhile applying a pressure differential of a higher pressure and a lowerpressure across the insert with the higher pressure being applied to theside of the upper or outer surface of the insert. The application of thepressure differential can be accomplished through use of a negativepressure (i.e., vacuum applied to the other (e.g., lower or inner)surface of the insert, or a positive pressure (i.e., pressure applied tothe outer surface of the insert), or a combination of the two. In someembodiments, the particulate material is deposited as a slurry under theapplication of a vacuum to the second (i.e., inner) surface of theporous insert.

The quantity and size of particulate material applied to the upper orouter surface of the porous insert (relative to the flow path of thecracked gas) can vary somewhat depending on the method utilized todeposit the particulate material. The primary goal in the application ofparticulate material is to completely cover the surface of the porousinsert that will ultimately support the dense gas selective (separation)membrane.

After the particulate material is placed in contact with the upper orouter surface of the porous insert to form a first coated surface anyexcess first particulate material that is present on the insert isremoved. The method of removal may vary depending upon the method ofapplication but in most instances it may be removed by friction (e.g.,mechanical or hand rubbing). In some embodiments, the step of removingthe excess particulate material is conducted while a vacuum is appliedto the lower or inner surface of the insert (the surface opposite theapplied particulate material). If the particulate material was depositedusing a wet process (e.g., slurry or suspension), the coated insertshould be dried prior to removing the excess particulate material toavoid removing slabs of wet particulate cake which may pull particulatematerial from the pores of the porous insert.

In some embodiments, the application of the particulate material(metallic components of a smaller particles size having an averageparticle diameter ranging, e.g., from about 0.001 to about 1 micron) maybe conducted to reduce the mean pore size of resulting coated poroussupport and to reduce the surface roughness of the porous support.Achieving these goals involves addressing several variables in theselection of the particulate material (e.g., choice of particulatematerial, method of application, particle size, etc.)

The deposition of the dense phase gas-selective membrane may be carriedout in one step or in multiple steps, and in some embodiments, withannealing after each step.

One useful method for annealing involves heat treating the coated poroussubstrate in an inert atmosphere at lower temperatures and thereafter inthe presence of hydrogen. More specifically, the annealing takes placein the absence of hydrogen until the annealing temperature is at least250° C., or at least 300° C., or for example, at least 350° C. Once theannealing temperature reaches 250° C., or for example 300° C., or forexample 350° C., hydrogen and oxygen can be present in the annealingstep. Stated alternatively, in some embodiments, the annealing step isconducted in a hydrogen containing atmosphere after the temperature hasreached a minimum of 300° C., for example at least 350° C. or forexample at least 400° C. Although the annealing step can be taken tovery high temperatures (e.g., 600° C. or greater), in most instances,the annealing step occurs at temperatures between 350° C. and 550° C.,or for example between 400° C. and 500° C. In embodiments where themembrane is built up by successive coatings, hydrogen is purged from thesystem as the membrane cools between deposition steps. In someembodiments, hydrogen is purged by flooding the system with an inert gasas the membrane starts to cool so that no hydrogen is present as themembrane reaches 300° C., for example, 400° C.

Inert gases that may be used in this heat treatment step includenitrogen, helium, argon, neon and carbon dioxide. The inert gas for usein the annealing step may be selected from nitrogen, argon, neon andcarbon dioxide. In one embodiment, the inert gas for use in the heattreatment is nitrogen.

The gaseous atmosphere under which the annealing step is conductedshould have some hydrogen in it once the annealing temperature reachesat least 300° C., or in some embodiments greater than 300° C. Thegaseous atmosphere used during the annealing step of the plated poroussubstrate should comprise a mixture of hydrogen from 3 to 100% and inertgas from 97 to 0%.

The annealing is conducted at a temperature that sufficiently treats thethin layer of gas-selective material (metal) that overlies the outersurface of the porous insert. While the required annealing temperaturedepends somewhat upon the particular metal or metal alloy that is platedupon the porous insert and the thickness of the layer thereof. In someembodiments, the heat treatment temperature should be in the range offrom at least 300° C. to 800° C. In some embodiments, the heat treatmenttemperature is in the range of from 325° C. to 700° C., or, in anotherexample, the heat treatment temperature is in the range of from 350° C.to 550° C.

The annealing step is conducted for a period of time sufficient toprovide the necessary treatment of the layer of gas-selective materialand where required prepare it for the next series of plating, polishingand annealing. The annealing time period may, thus, be in the rangeupwardly to 48 or more hours, but, a typical annealing time period is inthe range of from 0.1 hours to 12 hours. In some embodiments, annealingtime is minimized to such a time necessary to provide the treatment ofthe layer of gas-selective metal required to achieve the benefitsdescribed herein. It is expected that such a time period is in the rangeof from 0.2 to 10 hours, or even in the range of from 0.3 hours to 4hours.

The pressure under which the annealing is conducted can be in the rangeof from 0.5 atmospheres (absolute) to 20 atmospheres. In someembodiments, the heat treatment pressure is in the range of from 0.8atm. to 10 atm.

It is believed that the grain growth parameters of the deposited metalincreases membrane stability and helps it resist change at elevatedtemperatures. Encouraging grain growth by increasing the annealingtemperature appears to have a beneficial effect, particularly when thelayers of gas selective material are polished between deposition steps.The polishing step is discussed in more detail below. It is thought thatthere is some positive effect in polishing the grains to effectivelysmear them into the open pores and form a uniform metal layer. Gasseparation systems formed in such a manner have been observed to resistcracking at high operational temperatures.

After annealing, the porous insert with its annealed supported membranelayer is polished/abraded. The polishing improves the surface of thedeposited layer for further deposition by minimizing surfaceabnormalities and deformities and by filling openings such as cracks,pinholes and other imperfections that may be present in the thinmembrane layer. Exemplary abrading and polishing methods are disclosedin U.S. Pat. No. 8,167,976 issued May 1, 2012 in the name of Del Paggioet al., assigned to Shell Oil Company.

In a further embodiment, the gas selective membrane is formed from aninorganic polymeric precursor which is crosslinked by photo initiationand then pyrolysed.

In some embodiments, the method involves pyrolyzing thephoto-polymerized thin film so as to result in a ceramic membrane thatcontains substantially no oxide. “Substantially no oxide” means lessthan 5 wt. % oxide, or in some embodiments less than 2 wt. % oxide, orin further embodiments less than 0.5 wt. % oxide.

The materials further usefully employed fall into two categories: themonomeric or oligomeric ceramic precursors and the multifunctional thiolmonomers. The ceramic precursors of primary interest are vinylfunctionalized, inorganic-organic silazanes. The composition andfunctionality of the thiolated comonomer is another variable that can beused to control the crosslinked polymer product properties. Non-oxygencontaining alkane dithiols with varying chain lengths and tetrathiolsboth independently and in tandem are preferred in some embodiments.

Comonomer concentration (silazane/thiol), comonomer functionality (e.g.,dithiol vs tetrathiol and the ratio of the two when used in tandem), anddithiol chain length are system variables that allow for controlledmanipulation of the polymerization kinetics, network formationcharacteristics, and correspondingly, the final properties of thepolymer product.

Polymer films should be formed utilizing the photo-induced free-radicalstep-growth thiol-ene polymerization disclosed herein where the “ene”functionality is incorporated via the silazane ceramic precursor. Insome embodiments, polymerization is conducted on bulk materials, i.e.,no solvent is needed. In some embodiments, the common UV photoinitiator,2,2-dimethoxy-2-phenylacetophenone, can be used to adjust the initiationkinetics. A unique feature of these thiol-ene reactions is their abilityto self-initiate; therefore, the use of a separate photoinitiator isoptional, providing an additional level of control over the molecularcomposition and homogeneity of the polymer product.

The polymer material properties are intimately linked to the propertiesof the monomeric/oligomeric reactants, the polymerization mechanismutilized, the reaction conditions (temperature, atmosphere, initiationrate (irradiation intensity, initiator concentration, andself-initiating monomer concentration, and initiation wavelength(s))),and the extent of conversion of the reactive functionalities. All ofthese factors cumulatively dictate the polymerization kinetics and,correspondingly, the material and chemical properties of the polymerproduct and thus, its separation characteristics.

Formation of an amorphous ceramic membrane may be accomplished byheating and pyrolysis of the polymeric ceramic precursor fabricated viathe step-growth photo-polymerization described previously. Just as thepolymer fabrication conditions and kinetics play a large role inproperty determination, so do pyrolysis conditions and kinetics. Thus,an understanding of the dependence of the polymer/ceramicstructure/properties on the material's thermal history is essential, insome embodiments.

In some embodiments, pyrolysis of the crosslinked polymeric ceramicprecursors is conducted in several different atmospheres, namely, underair, vacuum, nitrogen, argon, and ammonia, where the atmosphere dictatesthe pyrolysis chemistry and thus, relative Si—C—N compositions in thefinal product with attainable compositions ranging from pure SiC to pureSi₃N₄. The heating rate, ultimate temperature, soak time at temperature,and cooling rate are also used, in some embodiments, to control thepolymer to amorphous ceramic transition and thus, the productproperties.

The systems and methods disclosed herein are, in some preferredembodiments, relevant to hydrogen separation. A recurring theme in theproduction of hydrogen is the separation of hydrogen from carbon dioxideor carbon monoxide and other minority components. There are a number ofprocesses where it would be advantageous to perform the separation usingmembranes at elevated temperatures. For example, in a water-gas-shiftreactor, removing the hydrogen at the temperature of reaction (200 to700° C.) would improve the efficiency of the process. The disclosureprovides robust ceramic membranes that will selectively transporthydrogen at up to 1000° C. and higher. This novel route utilizespreceramic polymeric precursors which gives one the ability to useestablished and economical polymer membrane fabrication techniques.

Some embodiments disclosed herein also address the long-standing issueof ceramic durability. Some bulk engineering ceramics prepared usingembodiments disclosed herein have proven to be much more robust thantraditional ceramics. This result is due, at least in part, to the finalcomposition of the ceramic, which is not obtained using standard ceramicfabrication techniques

In some embodiments, the gas-selective membrane may overlie anintermediate layer between the membrane and the substrate.

The intermediate layer includes particles and a binder metal. The bindermetal is uniformly distributed throughout the intermediate layer. Theterm “uniformly distributed,” as used herein, refers to a uniformdistribution of binder metal across the surface area of the particles ofthe intermediate layer. In one embodiment, the binder metal is ahydrogen-selective metal or an alloy thereof. “Hydrogen-selectivemetals” include, but are not limited to, niobium (Nb), tantalum (Ta),vanadium (V), palladium (Pd), platinum (Pt), zirconium (Zr) andhydrogen-selective alloys thereof. In some embodiments, palladium andalloys of palladium are preferred.

In some embodiments, the intermediate layer includes particles uniformin size, e.g., of uniform diameter. Alternatively, the intermediatelayer can include particles of varying sizes and/or size distributions.The intermediate layer can include blends and/or layering of differentparticles including particles of differing sizes. The intermediate layercan include a gradient of particle size from a surface of theintermediate layer proximate to the porous substrate (insert) to asurface of the intermediate layer distal to the porous substrate(insert). In one embodiment, particles having a smaller average sizeoverlie particles having a larger average size. For example, particleshaving a larger average size are located proximate to the poroussubstrate (e.g., inside the pores of the porous substrate) and particleshaving a smaller average size are located distal to the porous substrate(e.g., inside the pores of the porous substrate but closer to themembrane-side surface of the porous substrate).

In one embodiment, the particles can have an average particle diameterof at least about 0.01 micron such as at least about 0.1, 0.5, 1, or atleast about 5 microns. The particles can include particles capable offitting into pores of the porous substrate. In some embodiments, theparticles can have an average particle diameter of less than 5 micronssuch as less than 1, 0.5, 0.1, or less than 0.01 microns. In oneembodiment, the particles have an average diameter ranging from about0.01 to about 5 microns. For example, the particles can have an averagediameter ranging from about 0.01 to about 3 microns or about 0.3 toabout 1 micron.

In one embodiment, the intermediate layer includes sublayers ofparticles and binder metal, e.g., at least two sublayers of particlesand binder metal. For example, the sublayers of particles and bindermetal can include a first sublayer of a first population of particlesand a first binder metal and a second sublayer of a second population ofparticles and a second binder metal, wherein the first population ofparticles has a larger average diameter than the average diameter of thesecond population of particles and wherein the second sublayer overliesthe first sublayer. Thus, in one embodiment, the intermediate layerincludes a sublayer of particles having a larger average diameter and anoverlying sublayer of particles having a smaller average diameter. Forexample, the intermediate layer can include a sublayer of particleshaving an average diameter of about 0.3 to about 3 microns and anoverlying sublayer of particles having an average diameter of about 0.1to about 1 micron. Sublayers of particles and binder metal are notnecessarily distinct sublayers. For example, the intermediate layer caninclude a gradient of particle sizes in a binder metal. In oneembodiment, the intermediate layer includes a gradient of particle sizesranging from generally larger particles at a point proximate to theporous substrate to generally smaller particles at a point distal to theporous substrate.

The particles of the intermediate layer can include metal particles,metal oxide particles, ceramic particles, zeolite particles, andcombinations thereof, among others. For example, the particles caninclude such materials as tungsten, aluminum oxide, zirconia, titania,silicon carbide, chromium oxide, and combinations thereof. Suitablemetal oxide particles include, but are not limited to, aluminum oxide,titanium oxide, yttrium oxide, and chromium oxide. In some embodiments,the particles include aluminum oxide particles, e.g., alpha-aluminaparticles and/or gamma-alumina particles. The particles can include ablend or a layering of different particles including particles ofdiffering compositions and/or sizes. The particles of the intermediatelayer can have various morphologies and shapes. For example, theparticles can be ordered (e.g., crystalline) or amorphorus. In oneembodiment, the particles include spherical or mostly sphericalparticles.

In some embodiments, the particles can have a melting point higher thanthe melting point of the porous substrate (insert), e.g., a porous metalsubstrate. The intermediate layer can include particles having a meltingpoint higher than the melting point of the dense gas-selective membrane.For example, in one embodiment, the intermediate layer includesparticles having a melting point temperature higher than both themelting point temperature of the porous metal substrate and the meltingpoint temperature of the dense gas-selective membrane.

The intermediate layer may be deposited on the porous substrate byapplying the same methods for depositing the materials used to form thedense gas selective membrane.

There is at least one vent over the gas tight seal between the membraneand the wall of the transfer line. This permits the separated gas to beremoved from the transfer line. While a sweep gas could be used, it isnot recommended as this will result in further separation orpurification of the recovered stream.

In operation, the cracked gas leaves the cracker at a temperature fromabout 800° C. to about 950° C. and a pressure from about 100 to 110 kPa.In the transfer line, the temperature may fall as low as 450° C., but,in some embodiments, in the transfer line, the temperature is maintainedat at least 500° C. The temperature of the gas separation membranesshould be less than 900° C. to try to reduce coke formation on themembrane surfaces. When decoking, care should be taken not to expose themembranes to excessive temperatures which causes degradation of thetransport mechanism of the membrane.

The performance of the composite gas separation modules described hereincan be assessed by measuring hydrogen flux through the module duringoperation. For example, hydrogen flux through the composite gasseparation modules, in some embodiments, is at least about 4, 10, 20, orat least about 30 (m³/m²-hr)_(STP) at about 350° C. and with a hydrogenpartial pressure difference of about 1 bar. In at least one embodiment,hydrogen flux through the composite gas separation module is at leastabout 33.6 (m³/m²-hr)_(STP) at about 350° C. and with a hydrogen partialpressure difference of about 1 bar.

While hydrogen is one of the components that may be removed from acracked gas prior to further processing, it may also be desirable toremove at least some of the methane, carbon dioxide and carbon monoxide.It may also be desirable to minimize the diffusion of ethane andethylene through the membranes, in some embodiments, to as low aspossible, and, in some instances, the concentration of ethane andethylene in the permeate stream should be less than 10 wt %, or lessthan 5 wt. %, or for example less than 2 wt. %.

The off gases recovered from the transfer line may be disposed of in anynumber of ways. They could be fed back to the burners for the furnace tomake steam (high or low pressure) or they could be sent to a flarestack.

Demonstration of Concept

On line plant analysis of cracked gas at the exit of a transfer lineexchanger was as follows:

H2 34.96 mol % CH4 5.49 mol % C2H2 0.24 mol % C2H4 32.58 mol % C2H623.92 mol % C3s 0.66 mol % C4+ 1.07 mol % CO 78.12 Ppm CO2 14.93 Ppm_UNKNOWNS 1.05 mol %

The typical conditions at the exit of a TLE are a temperature in therange from 450° C. to 500° C. and a pressure of about 101 kPa.

Concurrently, a sample of gas from a port on the exit of the cracker waspassed through a stainless tube to cool it to about 450° C. to about500° C. The pressure of the gas was about 110 kPa. The sample of the gaswas separated through a ceramic frit comprising 97% alumina and about 3%MgO.

The permeate was analyzed using a gas chromatograph. The results are asfollows:

H2 39.25 mol % CH4 6.43% mol % C2H2 28.91 mol % C2H6 23.05 mol % C-3's0.73 mol % C-4's 0.70 mol % CO 0.04 mol % CO2 0.13 mol %

The frit was not tested for cracks and specific pore size. The test wasto see what differences in the compositions of gases might be. Thehydrogen concentration increased in the permeate. The test demonstratesa proof of concept.

The present disclosure provides a method to partially reduce the load ofH₂, CH₄, CO and CO₂ exiting a transfer line of a steam cracker reducingthe load on the down-stream separation train of the steam cracker.

What is claimed is:
 1. A transfer line between an outlet of a steamcracking furnace and an inlet to a quench exchanger comprising: i) acontinuous passageway of a metal having a melting temperature greaterthan 1000° C. having a flange at one end of the passageway adapted tocooperate with the outlet from the steam cracking furnace and a flangeat the opposite end of the passageway adapted to cooperate with theinlet to the quench exchanger; one or more inserts in said passagewaypermitting a flow of gases through said passageway, said inserts beingpermeable to at least one of H₂, CH₄, CO, and CO₂ at temperatures from500° C. to 900° C. and spaced from an interior wall of the passagewayand sealed to the interior wall of said passageway to provide one ormore gas tight chambers; and one or more ports through the metal towithdraw gases from said one or more gas tight chambers; said insertsbeing selected from a) ceramic inserts having a melting point greaterthan 900° C. and a porosity from 5 to 75% of pores having a size from0.001 microns to 0.5 microns and fitting within the metal casting and b)metal inserts having a porosity from 5 to 75% of pores having a sizefrom 0.001 microns to 0.5 microns; c) or both; and optionally ii) amembrane permeable to at least one of H₂, CH₄, CO, and CO₂ attemperatures from 500° C. to 900° C. on said inserts to permit thepassage of at least one of H₂, CH₄, CO, and CO₂ there through into thegas tight chamber.
 2. The transfer line according to claim 1, whereinthe insert is a porous ceramic formed from oxides, dioxides, nitrides,carbides and phosphates selected from porous silicon dioxide, fusedsilicon dioxide, porous aluminum oxide, titanium dioxide, zirconiumdioxide, thorium dioxide, lanthanum oxide, magnesium oxide, calciumoxide, barium oxide, tin oxide, cerium dioxide, zinc oxide, boron oxide,boron nitride, boron carbide, boron phosphate, zirconium phosphate,yttrium oxide, aluminum silicate, silicon nitride, silicon carbide andmixtures thereof.
 3. The transfer line according to claim 1 wherein theinsert is resistant to coking.
 4. The transfer line according to claim1, wherein the insert is in the shape of a cone or an island.
 5. Thetransfer line according to claim 1, wherein the insert is a metal alloycomprising one or more of iron, nickel, titanium, chromium, aluminum,chromium, nickel and molybdenum.
 6. The transfer line according to claim1, wherein the membrane is present and has a thickness from 0.1 to 10microns.
 7. The transfer line according to claim 1, wherein the membraneis present and the membrane comprises one or more metals selected fromPd, Ta, V, Pt, Nb, and Zr.
 8. The transfer line according to claim 7,wherein the membrane further comprises one or more metal oxide ceramicselected from Al₂O₃, BaTiO₃, SrTiO₃ and ZrO₂.
 9. The transfer lineaccording to claim 8, wherein the membrane is a dense metal oxidemembrane.
 10. The transfer line according to claim 9, wherein in themembrane the metal comprises Pd.
 11. The transfer line according toclaim 10, wherein the metal oxide comprises yttria stabilized ZrO₂. 12.The transfer line according to claim 10, wherein the metal oxidecomprises calcia stabilized ZrO₂.
 13. The transfer line according toclaim 9, wherein the membrane is not less than about 95% of theoreticaldensity.
 14. The transfer line according to claim 8, wherein themembrane is coated on component a).
 15. The transfer line according toclaim 14, wherein component a) comprises an alumina ceramic.
 16. Thetransfer line according to claim 8, wherein the membrane is coated oncomponent b).
 17. The transfer line according to claim 8, whereinintermediate the ceramic oxide and component b) is a ceramic comprisingone or more particles selected from tungsten, alumina oxide, zirconia,titania, silicon carbide, chromium oxide, yttrium oxide, having aparticles size from 0.01 to 5 microns.
 18. The transfer line accordingto claim 1, wherein the membrane is Si/C/N ceramic formed by: combininga monomeric and/or oligomeric silazane ceramic precursor with acomonomer comprising one or more of the group consisting of ene (vinyl)functionalized, oligomeric, inorganic or organic silazanes, difunctionalthiols, and tetrafunctional thiols; forming the combination as a thinfilm on a substrate; photopolymerizing the thin film; and pyrolyzing thephotopolymerized thin film so as to result in a ceramic membrane thatcontains substantially no oxide.
 19. The transfer line according toclaim 18, wherein said monomeric and/or oligomeric silazanes containheteroatoms selected from boron, titanium, aluminum, phosphorus, andcombinations thereof.
 20. A cracking furnace and quench system forcracked gases comprising intermediate the exit of the cracking furnaceand the quench system a transfer line according to claim 1.